1. Field of the Invention
The invention relates to a vehicle brake system; and more specifically, to a brake system having a service brake system and a parking brake system.
2. Description of Related Art
A motor vehicle generally has two front wheel brakes arranged in the region of a front axle of the motor vehicle and two rear wheel brakes arranged in the region of a rear axle of the motor vehicle. In addition, the motor vehicle may include a hydraulic system supplying the wheel brakes with a hydraulic fluid for the operation thereof. The hydraulic system including electrically actuated valves. The motor vehicle may also include a parking brake system that activates the rear wheel brakes.
The motor vehicle may be equipped with diverse driving assistance systems. In particular, the vehicle may have an emergency brake system, wherein upon detection of a hazardous situation the system conducts autonomous emergency braking of the motor vehicle. The emergency brake assistant system may include an electronic brake control operative to signal the hydraulic system whereby the hydraulic system operates to build hydraulic pressure, for example brake fluid pressure, and supply the wheel brakes with the pressurized hydraulic fluid. The motor vehicle may also include a hill start assist (HSA) system wherein a motor vehicle having manual or automatic transmission shifting and which is standing on an inclined carriageway is temporarily held to prevent inadvertent rolling away of the motor vehicle and to facilitate starting. Such a hill start assist system may include an electrically actuated parking brake system.
Larger and heavier motor vehicles customarily have a brake system of larger dimensions, in particular larger brake cylinders, than smaller and lighter motor vehicles. A greater amount of hydraulic fluid must be fed to the larger brake cylinders than is the case with smaller brake cylinders. Brake pressure generally builds up more slowly with correspondingly larger and heavier motor vehicles than with smaller and lighter motor vehicles. To compensate for this, a hydraulic system of a larger and heavier motor vehicle can be provided with a larger and more powerful fluid pump, but this is associated with weight disadvantages.